Creatures of the deep usually found in the more balmy waters of the Mediterranean or the Pacific are finding their way into Scottish seas as a result of climate change.

Fishermen in the Western Isles are reporting a boom in unusual fish and molluscs rarely seen in the area before. They have revealed that thousands of octopuses, migrating north in ever increasing numbers as sea temperatures rise, are ending up in their lobster creels. In fact, climate change has appeared to have warmed Scottish waters to such an extent that squid, deep-sea John Dory fish, red blenny and Japanese skeleton shrimp are also being caught by fishermen. The colourful variety of species are being studied by marine scientists north of the border.

In the Outer Hebrides creel fishermen are catching so many octopuses that they are now selling the former Mediterranean delicacy for the same price as cod.

'Where once fishermen were lucky to see, let alone catch an octopus, now they are finding up to 300 a time as the creatures invade the creels in search of the same bait that is sued to attract lobsters and crabs,' said Duncan MacInnes, secretary of the Western Isles Fisherman's Association.

Although, at around 2ft long, the West Coast octopuses are much smaller than their 10ft Mediterranean cousins or 30ft Pacific relations, creel fishers to the west of Lewis are still catching enough to make a profit even though they would rather have more lucrative lobsters.

'Those who are creel fishing to the west of Lewis are reporting a significant increase in octopus this year,' added MacInnes. 'In a day they will catch up to 50 kilos of octopus in a day. They only used to see two or three in a year, but something's happened and there's an awful lot more now.

'The fishermen reporting it are fishing to the Atlantic side of the Hebrides, but the trawlers to the eastern side of the Hebrides are also reporting seeing octopuses as they come closer to shore.

'Despite the growing market for the octopus the fishermen aren't entirely happy with the development because they go into the baskets and eat the more valuable lobsters.' Further out to sea fishermen are reporting a similar boom in squid fishing around the remote uninhabited North Atlantic isle of Rockall.

MacInnes went on: 'There seems to have been a shift of marine species. Creatures that only used to be found further south are appearing in more northern latitudes in much greater numbers than previously. The squid fishing has been very good at Rockall this year and they haven't appeared there for about 20 years.

'The squid are part of the same family as the octopus so it's a bit too much of a coincidence. It certainly seems to suggest that the seas are getting warmer. It's more than likely to be global warming, which could also mean that some of the species that are more traditional to these waters have moved further north.

'Cod, for example, is a cold-water species and although people say that it's in decline because of over-fishing, it could, in fact, be because it has moved north as the water of its traditional habitat warms.'

The Scottish Association for Marine Science, based in Oban, has been studying the change in the temperature of the water with particular interest and the number of alien species that are arriving and surviving in an environment that was previously uninhabitable for them.

'The waters are certainly getting a warmer. Species that would have been typical for the south coast are now moving increasingly northwards,' said Dr. Anuschka Miller, a spokeswoman for The Scottish Association for Marine Science.

'We've been looking at the Japanese skeleton shrimp in particular. It's a very powerful and successful invader which has spread from the Pacific to be here and the water is certainly warm enough for them.

'It is part of a wider trend; we're seeing a lot of alien species coming in from other parts of the world. Some are connected to ship hulls or even come in with other agricultural products. When they arrive they aren't dying off from cold as they once did, the conditions that exist now mean they can survive longer.'

Miller said there had even been species from Australia that had attached themselves to a ships hull and then produced eggs in Oban harbour: 'In the past most of these alien organisms would die off within the year when the water gets too cold for them. However, as the waters warm up a lot of these species will be able to establish themselves causing quite a shift in speciation.'